1. Field of the Invention
The present invention relates to a positive resist composition. More particularly, the present invention relates to a positive resist composition which is sensitive to ultraviolet light, far ultraviolet light including excimer laser, electron beam, ion beam, X-ray and the like.
2. Description of the Related Art
A composition containing a compound having a quinone diazide group and an alkali-soluble resin finds use as a positive resist because, upon exposure to light having a wavelength of 500 nm or shorter, the quinone diazide group decomposes to form a carboxyl group whereby the originally alkali-insoluble composition becomes alkali-soluble. Since the positive resist composition has much better resolution than a negative resist composition, it is used in the production of integrated circuits such as IC or LSI.
Recently, particularly with integrated circuit, miniaturization has proceeded with a rise in the integration level, which results in demands for formation of patterns of submicron order. To satisfy such demands, a step-and-repeat type reduction projection exposure apparatus, namely a stepper is used as an exposure apparatus. When a numerical aperture (NA) of a reduction projection lens of the stepper is increased, a resolution is increased while a depth of focus is decreased. Because of the step-and-repeat type, a throughput of the stepper is smaller than that with a batch exposure system. Therefore, the positive resist composition is required to have a much improved depth of focus and sensitivity in addition to good resolution, .gamma.-value, profile and coating properties.
With the increase of the integration level of LSI, a distance between pattern lines is greatly decreased. To this end, etching is carried out mainly by dry etching in place of conventional wet etching. Therefore, the resist is required to have improved heat resistance.
When the currently used positive resists are checked from the above view points, they do not necessarily have the satisfactory depth of focus, sensitivity and heat resistance. In addition, the currently used resist tends to leave a developing residue (scum) on developed areas at a critical resolution, or provide a non-rectangular profile.